Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Voyager Homepage, http://voyager.jpl.nasa.gov/index.html

An alignment of the outer planets that occurs only once in 176 years prompted NASA to plan a grand tour of the outer planets, consisting of dual launches to Jupiter, Saturn and Pluto in 1976-77 and dual launches to Jupiter, Uranus and Neptune in 1979. The original scheme was canceled for budgetary reasons, but it was replaced by Voyager 1 and 2, which accomplished similar goals at significantly lower cost.

The two spacecraft were designed to explore Jupiter and Saturn in more detail than the two Pioneers (Pioneers 10 and 11) that preceded them. Each was equipped with slow-scan color TV to take live television images from the planets, and each also carried an extensive suite of instruments to record magnetic, atmospheric, lunar, and other data about the planets. The original design of the spacecraft was based on that of the older Mariners. Power was provided by three plutonium oxide radioisotope thermoelectric generators (RTGs) mounted at the end of a boom.

Voyager 1 was launched after Voyager 2, but because of a faster route, it exited the asteroid belt earlier than its twin. It began its Jovian imaging mission in April 1978 at a range of 265 million km from the planet; images sent back by January the following year indicated that Jupiter's atmosphere was more turbulent than during the Pioneer flybys in 1973 and 1974.

On 10 February 1979, the spacecraft crossed into the Jovian moon system, and in early March, it had already discovered a thin (less than 30 km thick) ring circling Jupiter. Flying past Amalthea, Io, Europa, Ganymede, and Callisto (in that order) on 5 March, Voyager 1 returned spectacular photos of their terrain, opening up completely new worlds for planetary scientists to study. The most interesting find was on Io, where images showed a bizarre yellow, orange and brown world with at least eight active volcanoes spewing material into space, making it one of the most (if not the most) geologically active planetary bodies in the solar system. The spacecraft also discovered two new moons, Thebe and Metis. Voyager 1's closest encounter with Jupiter was at 12:05 UT on 5 March 1979 at a range of 280,000 km.

Following the Jupiter encounter, Voyager 1 completed a single course correction on 9 April 1979 in preparation for its rendezvous with Saturn. A second correction on 10 October 1979 ensured that the spacecraft would not hit Saturn's moon Titan. Its flyby of the Saturn system in November 1979 was as spectacular as its previous encounter. Voyager 1 found three new moons: Prometheus and Pandora, the shepherding moons that keep the F ring well-defined, and Atlas which similarly shepherds the A ring. It also discovered a new ring (the G ring) and revealed the intricate structure of the ring system, consisting of thousands of bands.

During its flyby, the spacecraft photographed Saturn's moons Titan, Mimas, Enceladus, Tethys, Dione, and Rhea. Based on data, all the moons appeared to be largely composed of water ice. Perhaps the most interesting target was Titan, which Voyager 1 passed at 05:41 UT on 12 November at a range of 4,000 km. Images showed a thick atmosphere that completely hid the surface. The spacecraft found that the moon's atmosphere was composed of 90 percent nitrogen. Pressure and temperature at the surface was 1.6 atmospheres and -180 degrees Celsius (-292 degrees Fahrenheit), respectively.

Voyager 1's closest approach to Saturn was at 23:45 UT on 12 November 1980 at a range of 124,000 km. The spacecraft found that about 7 percent of the volume of Saturn's upper atmosphere is helium (compared with 11 percent of Jupiter's atmosphere), while almost all the rest is hydrogen. Since Saturn's internal helium abundance was expected to be the same as Jupiter's and the sun's, the lower abundance of helium in the upper atmosphere may imply that the heavier helium is slowly sinking through Saturn's hydrogen. That might explain the excess heat that Saturn radiates over energy it receives from the sun.

Following the encounter with Saturn, Voyager 1 was on course to escape the solar system at a speed of about 523.6 million km (325.4 million miles or 3.5 AU) per year in the general direction of the sun's motion relative to nearby stars. The spacecraft's trajectory, which had been designed to send it closely past Titan and behind Saturn's rings, bent the spacecraft's path inexorably northward, 35 degrees out of the ecliptic plane, the plane in which the planets orbit the sun. Thus, Voyager 1 could not be sent to Uranus or Neptune.

The official goal of the Voyager Interstellar Mission (VIM), as the dual Voyager flights have been called since 1989, is to extend NASA's exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the sun's sphere of influence, and possibly beyond. Specific goals include collecting data on the heliopause boundary, the outer limits of the sun's magnetic field and the outward flow of the solar wind.

On 17 February 1998, Voyager 1 became the most distant human-made object when it surpassed Pioneer 10's range from Earth. In September 2013, Voyager 1 was 19 billion km (12 billion miles) from our sun. Earlier that same year (August 2012), Voyager 1 passed into interstellar space.

Voyager 1 is speeding along at about 57,600 kph (35,790 mph) -- fast enough to travel from the Earth to the sun three and a half times in one year.

Both Voyagers carry a gold record "greeting to the universe" (right) containing sounds and images selected to portray the diversity of life and culture on Earth.

Voyager 1 is escaping the solar system at a speed of about 523.6 million km per year, or about 1.4 million km per day and is now in interstellar space (as of Aug. 2012).

Even at this tremendous speed, Voyager 1 will take at least 14,000 years (and maybe twice that or even longer) to emerge from the Oort cloud.

Did you know that the record is a 30-cm gold-plated copper disc? Together with a needle and playing instructions, it is mounted on the body casing and on it are recorded natural Earth sounds, 90 min of music, 115 pictures, and greetings in 60 languages.